Flux and method of coating ferrous article

ABSTRACT

THIS INVENTION RELATES TO THE PROCESS OF COATING FERROUS ARTICLES BY THE MOLTEN METAL IMMERSION METHOD, MORE PARTICULARLY TO THE PROVISION OF AN AQUEOUS FLUX APPLIED TO SAID ARTICLE PRIOR TO THE METAL COATING THEREOF. SPECIFICALLY, THE PROCESS INCLUDES CLEANING THE FERROUS ARTICLES, WETTING THE SURFACES WITH AN AQUEOUS FLUX OF FLUOSILICIC ACID, WITH UP TO FOUR COMPOUNDS FROM THE GROUP CONSISTING OF HYDROCHLORIC ACID, HYDROFLUORIC ACID, POTASSIUM FLUORIDE AND ZINC CHLORIDE, DRYING SAID FLUX ON THE SURFACE, IMMERSING SAID ARTICLE IN A MOLTEN METAL BATH CONSISTING ESSENTIALLY OF AT LEAST 25% BY WEIGHT ALUMINUM, BALANCE ESSENTIALLY ZINC, AND AFTER REMOVAL FROM THE BATH, SHAKING OFF EXCESS METAL AND COOLING TO YIELD A FERROUS ARTICLE HAVING A CONTINUOUS AND ADHERENT LAYER OF SAID ALUMINUM ALLOY.

United States Patent O 3,806,356 FLUX AND METHOD OF COATING FERROUSARTICLE Carlyle E. Shoemaker, Bethlehem, Pa., assignor to Bethlehem,Steel Corporation, Bethlehem, Pa. Filed Aug. 9, 1972, Ser. No. 275,610Int. Cl. C23c 1/08; C23f 17/00 US. Cl. 117-50 11 Claims ABSTRACT OF THEDISCLOSURE essentially of at least 25% by weight aluminum, balanceessentially Zinc, and after removal from the bath, shaking off excessmetal and cooling to yield a ferrous article having a continuous andadherent layer of said aluminum alloy.

BACKGROUND OF THE INVENTION This invention is directed to the concept ofcoating ferrous metal articles, by the hot metal immersion method, toenhance the articles appearance and resistance to corrosion attack. Toeffect such results, an adherent and continuous layer of a corrosionresistant material on the ferrous article is essential. The prior artusing various combinations of salts and acid has met with limitedsuccess in galvanizing and aluminizing processes due to productioncosts, processing controls and product performance.

Typically, the ferrous article to be coated had to be cleaned of' greaseand scale (oxides of iron) prior to the application of the metalliccoating. In a continuous strand operation, i.e. strip or wire, thematerial preferably is cleaned and then bathed in an oxide reducingatmosphere, and without exposing it to the atmosphere is immediatelyimmersed in a molten metal bath containing the coating metal. For batchoperations, particularly for large structural members, atmosphericexclusion is virtually impossible. Accordingly, alternatives forprotecting the cleaned surfaces were found. Generally, the procedure wasto apply athin flux coating following the cleaning, and then immersingthe flux coated ferrous article into the molten metal bath. Naturally,the nature of the fluxing composition is important to its effect on theferrous base, for its ability to provide a proper surface for thereception of a metal coating, which is both continuous and adherent.Thus there is a relationship between the flux and coating metal.

While the prior art has made some significant contributions in the areaof galvanizing and aluminizing, such efforts have not been totallysatisfactory forpreparing ferrous surfaces for the reception of analuminum-zinc coating. However, with the discovery of a fluosilicic acidcontaining flux, an effective means was found to prepare the surface ofa ferrous article for subsequent coating by an aluminum-zinc alloy.

3,806,356 Patented Apr. 23, 1974 "ice SUMMARY OF THE INVENTION Thisinvention relates to the process of coating ferrous articles by themolten metal immersion method, more particularly to the provision of asuitable aqueous flux containing fluosilicic acid for applying to thesurfaces of the ferrous article prior to the metal coating thereon. Inits preferred embodiment, said process includes cleaning the ferroussurfaces to remove grease, etc., pickling to remove scale, dippingdirectly into a flux bath containing from about 2 to about 15% byweight, H SiF with up to about a total of 25%, by weight of the fluxbath, of the compounds from the group consisting of HCl, HF, KF, and ZnC1 where the quantity of said compounds depends on the alloy content ofthe ferrous article, drying the flux in situ, and immersing the fluxcoated ferrous article in a molten metal bath of at least 25% by weightaluminum, balance essentially zinc. Upon withdrawal from the moltenbath, and removal of excess metal, such as by bumping, the metalliccoating solidifies to produce a ferrous article having a continuous,adherent coating of an aluminumzinc alloy.

BRIEF DESCRIPTION OF THE DRAWING The figure is a flow sheet illustratingthe preferred sequence of steps followed in carrying out the process ofthis invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to a moredetailed review of the invention, as set forth in the illustrated flowsheet of the figure, it will be seen that the present invention providesan improved hot metal immersion coating procedure yielding a ferrousarticle having a continuous, adherent coating of an aluminum-zinc alloythereon.

The coating method generally comprising wetting the cleaned scale freeferrous article with an aqueous solution containing from about 2 to 15by weight, H SiF with up to a total of about 25 by weight, of thecompounds selected from the group consisting of HCl, HF, KF, and ZnClFollowing the wetting thereof, the ferrous article is dried such as byheating to a low temperature of up to about 400 F. to remove all signsof dampness. This is important, especially from a safety standpoint, toavoid splashing of the subsequently applied molten coating metal.

The dry flux coated ferrous article is then immersed for from 2 to about5 minutes, depending on the depth of metallic coating desired, in amolten metal bath containing at least 25 by weight, aluminum, preferablyup to about balance essentially zinc. After removal, excess coatingmetal is removed, such as bumping or agitating the coated ferrousarticle, where it may be cooled by air or water quenching. The resultingproduct exhibits a continuou's, adherent alloy coating on the processedferrous article.

At this juncture, it should be made clear that as used herein, the termarticle is intended to include strip and wire (treated in a continuousmanner), and shapes, such as structural members treated in a batchprocess. Actually, the greatest benefits from this invention arerealized in the batch treatment of ferrous shapes, such as largestructural steel members used in the construction industry. Though notlimiting, the further description and exemplary showings shall bedirected to batch operations.

Optimum results, particularly in the treatment of alloy structuralsteels, were observed with fluxing compositions containing from about4.0 to 8.0%, by weight, H SiF 3 .7 r :4 and about 5.0 to 20.0%, byweight, of a plurality of the consisting essentially of fluosilicicacid, and up to four remaining compounds listed above. For example, fromcompounds from the group consisting of hydrochloric acid the standpointof coating coverage, adherence and appearhydrofluoric acid, potassiumfluoride and zinc chloride, ance, a preferred fiuxing composition is asfollows: removing said article from the aqueous acidic figx, drying qsaid article by heating to a low temperature, an immersg g Percent by g5 ing the article in a molten bath containing said aluminumi 6 zinccoating alloy. KF The method claimed in claim 1 wherein the fluozncl dL8 silicicacrd is present in amount between about 2 to V Balance 10 byweight, of said aqueous flux.

- n V 3. The method claimed in claim 2 wherein at least one To furtherillustrate the effectiveness of the fluxing comof said four compounds ispresent up to a total amount of position on surface coverage,evaluations were made on by weight, of said aqueous flux. two commongrades of structural steel, with variations in 4. The method claimed inclaim 2 wherein said fluofiux composition. The said variations arelisted in Table I, 15 silicic acid is present in an amount between about4 to 8%. with the results in Table II. 5. The method claimed in claim 4wherein at least one TABLE I Flux baths, weight percent A B C D E F G HJ K L M N P Q Components:

TABLE II Percent surface covered, 5 minutes dip A B C D E F G H .T K L MN P Q While it may be gleaned from the foregoing tabulaof said fourcompounds is present in an amount between tion, as it pertains toalloyed steels, optimum results or about 5 to 20%, by weight, of saidaqueous flux. surface coverage were noted with the richer fluxes, i.e.6. The method claimed in claim 5 wherein a plurality those containing aplurality of said compounds. However, of said four compounds are presentin said aqueous flux. with leaner ferrous articles, such as mild or lowcarbon 7. The method claimed in claim 5 wherein at least steels, simplerflux combinations, with the components 40 three of said four compoundsare present in said aqueous named, may be formulated. flux.

For instance, aqueous fluosilicic acid may be used alone 8. A flux forthe treatment of a ferrous article prior to or in combination with onlyone or two of the remaining its immersion in a molten bath containing analuminumcomponents. Some combinations which have been found zinc alloy,comprising an aqueous acidic solution consuitable for mild carbon steelsheet and strip are listed sisting essentially of from 2 to 15%, byweight, of fluobelow. silicic acid, and a total of from 5 to 20%, byweight, of

' at least one compound selected from the group consisting TABLE In ofhydrochloric acid, hydrofluoric acid, potassium fluoride, and zincchloride. f if g gg 9. The flux claimed in claim 8 wherein saidfluosilicic N P Q acid is present in an amount between about 4 to 8%.

10. The flux claimed in claim 9.wherein a plurality of said fourcompounds are present in the aqueous fluxQ i jjj"jjj 11. The fluxclaimed in claim 10 wherein at least three g 10 of said four compoundsare present in the aqueous flux. I

References Cited Since the foregoing represents the preferred embodi- UITE STATES PATENTS merits of this invention, it is contemplated thatvariations 2 571,737 3 1954 jominy et 1 1172.51 may be effected hereinby those skilled in the art, par- 2 907 104 1 959 Brown et 1 9 ticularlyafter reading these specificatiions. accordingly, 2 174 551 10 1939Cinamon et 1 117 5.2 no limitation is intended to be impose on t 'sinvention except as set forth in the appended claims. FOREIGN PATENTS 1l i 1,025,603 4/1966 Great Britain 117-52 1. A method of forming acontinuous alloy coating consisting of from 25% to about by weightalumi- RALPH KENDALL, Pflmafy Exflmlller num, balance essentially zinc,on a ferrous article, com- W. BALL, Assistant Examiner prising the stepsof cleaning said ferrous article to re- U S C1 XR move grease and oxidesfrom the surfaces thereof to be 70 coated, immersing said article in anaqueous acidic flux 117 -50, 114 C, 114 A; 14823

